In the field of mechanical transmission, gears are widely used. When the gears are meshed with each other to transmit speed and torsion, if a main gear drives a pinion, a rotating speed of the pinion will be increased, but driving force given by the main gear is greater than output force of the pinion; if the pinion is used to drive the main gear, a rotating speed of the main gear will be reduced, but driving force given by the pinion is less than output force of the main gear. So if it is desired to maintain a relatively high torsion, the rotating speed needs to be reduced correspondingly. A common technology is reducing the speed and increasing the torque. Persons skilled in the mechanical industry generally desire to improve the transmission efficiency of the existing gears, with main approaches of: 1) improving the accuracy; and 2) decreasing the friction of gear meshing.